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Two-stroke Engine vs Four-stroke Engine

Throughout the history of engine design, there have been two main combustion engine types – 2-stroke engine and the 4-stroke engine. These terms may have left you wondering, what is the difference between them and which one of these is better in terms of efficiency and maintenance. If you are in the market for a new engine, here is what you need to know in terms of efficiency and maintenance.

Difference Between a Two-Stroke Engine and a Four Stroke Engine

The main difference between a two-stroke engine and a four-stroke engine lies in the way they operate.

Two Stroke Engine

In a two stroke engine, the combustion cycle is completed with two strokes: a compression stroke followed by the power stroke. During the return stroke, the exhaust is let out, and a fresh mixture of fuel and air enters the combustion chamber. The spark plug fires once in every single revolution.

How does it work?

  • Fuel and air are compressed in the cylinder (compression stroke).
  • The spark plug ignites the fuel-air mixture causing an explosion that drives the piston downwards. (power stroke)
  • As the piston nears the end of the cylinder, the exhaust port is uncovered. (power stroke)
  • As the piston reaches the bottom of the cylinder, the inlet port introduces more fuel and air and starts the process again. (compression)

Four Stroke Engine

In a four stroke engine, piston completes two strokes during each revolution. The spark plug fires only once every revolution. These engines do not require pre-mixing of fuel and oil, as they have a separate compartment for the oil.

How does it work?

  • The piston moves up and compresses the fuel-air mixture in the chamber (compression stroke)
  • The spark plug ignites the compressed air and provides adequate momentum to keep the crankshaft turning (power stroke)
  • When the piston moves back up, the burnt gases are sent out through the exhaust valve (exhaust stroke)
  • The piston moves back down and draws a fresh fuel-air mixture and compresses the mixture in the chamber. (intake stroke)

Which is Better?

  • In terms of efficiency, a 4-stroke engine wins because fuel is consumed once in every four strokes.
  • A four-stroke engine weighs heavier. It weighs 50% more than a two-stroke engine.
  • A four-stroke engine is less noisy. A two-stroke engine is louder and has a distinctive high pitched buzzing noise.
  • Four-stroke engines are more durable.
  • A four-stroke engine is more ecofriendly. The exhaust in two-stroke is released into the air.
  • In comparison to a four-stroke engine, a two-stroke engine is easier to repair because of its simple design. However, frequent repairs are needed for a two-stroke engine unless you actively maintain it.

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